Len is right as far as he went. The c1 setting in the menu system controls whether the shutter release acts as an AE-L button on the D4 or not. I personally don't want the shutter release to act as my AE-L button. Except for wildlife photography, I use the shutter release to activate autofocus, and lock in focus when the shutter release is halfway down. At that point, I want to be able to reframe my shot, and that may very well mean the exposure at the focus point is the incorrect exposure. Hence I have separated activation of focus lock and exposure lock. (Even when I'm doing wildlife photography, and I use the AF button to activate autofocus, so if I also use manual focus when I press the shutter release down, it doesn't alter the focus, I don't use the shutter release to exposure lock.)
Therefore, for me, c1 is set to OFF.
On the other hand, there are times when I want to lock in my exposure, then reframe. So I need a button assigned to be able to activate exposure lock.
On my D4, I've set f6 on the menu system, "Assign Sub-Selector Center," to AE lock only. So, if I want to lock my exposure I merely press and hold my Sub-Selector Center button.
So, if I want to lock both focus and exposure, when shooting anything but wildlife (For wildlife focus is automatically locked as long as I don't press my AF button.) I press the shutter release halfway down, and the Sub-Selector Center button in and hold them both. That's easily accomplished with my right hand index finger (shutter release) and thumb (Sub-Selector Center button).
Thank you- I will experiment with this... It looks like the way to lock the AE. I played w/ Len's method but I could not get it to lock. Each time I pulled my finger off the shutter button it released the setting.
That's how it's supposed to work with the shutter release button. It works the same way to autofocus lock. You hold the shutter release halfway down and it's locked until you either let go, or press the shutter release all the way down taking the photo with the locked settings.